1. Technical Field
Systems and methods for controlling an internal combustion engine to manage induction air acoustics.
2. Background Art
Customer expectations for engine/vehicle sounds generally vary based on the type of vehicle and relative engine/vehicle output, with louder sounds expected or tolerated at higher engine outputs. Internal combustion engine valve train technologies developed to improve fuel economy, such as electromagnetic valve actuation (EVA), can control airflow by changing valve timing and opening the electronic throttle valve to reduce pumping losses and increase engine efficiency. However, this often increases sound levels associated with induction air that may exceed some customer's expectations under various operating conditions and may therefore be undesirable. One known strategy used to manage acoustics associated with induction air includes closing the electronic throttle in response to a manifold pressure (MAP) sensor to create a manifold vacuum. However, this solution depends on the particular throttle body flow characteristics and provides acceptable results at moderate manifold vacuums, but is difficult to control at lower manifold vacuums and low to moderate engine speeds, particularly in variable displacement engines that may operate on fewer than all of the cylinders with active cylinders operating at full load. For example, when operating in a lower displacement mode with 4 or 6 active cylinders of an 8 cylinder engine, the total engine output is an average of the active and inactive cylinders although each running cylinder operates at full load (low manifold vacuum) to maximize efficiency and fuel economy benefits. Under these conditions controlling the throttle to a target manifold pressure using feedback and/or feed-forward control based on manifold pressure does not provide acceptable acoustic control because small throttle valve angle changes can increase induction sound levels without a corresponding increase in manifold pressure.